Such a sealing device of a known type is shown in FIGS. 1 and 2 on the accompanying drawing, in which FIG. 1 shows a section through the center line of the device; and FIG. 2 shows an enlarged view of a portion of FIG. 1.
In FIGS. 1 and 2, an inner sleeve 1 and an outer sleeve 2. are made of metal and together form a bushing or support for a pump shaft 3. They define an annular slot 4, the opening of which faces the shaft 3. The slots walls comprise two conical annular surfaces 5 and 6, which converge in a radially inward direction so that slot 4 is trapezoidal in cross-section. A sealing ring 7 of rubber or a similar resilient, elastomeric material is arranged in the radially inner part of the slot 4. Radially outside the sealing ring, the slot 4 is connected to a channel 8 for the supply of a pressure medium, for example oil. The rubber ring 7 is formed with ring surfaces which are pressed against the conical ring surfaces 5 and 6 of the slot when channel 8 is connected to a pressure source. At the same time the radially inner surface of the rubber ring is pressed against the pump shaft 3 and seals thereagainst. Thereafter, the space above or below the rubber ring can be evacuated. When the pump is to be started, the rubber ring 7 is first relieved of pressure to avoiding abrasion thereof.
The drawback of this prior art seal is that during long periods of pressurization the rubber ring will creep in such a manner that part of the rubber material, initially disposed within the edges of the slot, will successively pass beyond these edges and accumulate outside the slot, as suggested in FIG. 2. Then when the pump is to be started and the contact between the rubber ring and the pump shaft is to be broken, this may not be possible because of the above-mentioned creep of the rubber. When the shaft 3 rotates, the rubber ring is destroyed.